The present invention relates to a device for magnifying the amount of deformation occurring in a piezoelectric element
Generally, when voltage is applied to the piezoelectric element, it is distorted to be deformed. Such deformation is greatly responsive to time, and a force to be generated by the deformation is large. Therefore, the piezoelectric element has superior chracteristics as a driving force for generating a mechanical displacement.
However, as the amount of deformation of the piezoelectric element is generally small, it is necessary to magnify such a small deformation of the piezoelectric element and convert the same into a large amount of displacement when it is used as the driving source. In the circumstances, there have been proposed various devices for magnifying the small deformation of the piezoelectric element and converting the same into the large amount of displacement (which devices will be hereinafter referred to as a piezoelectric actuator).
FIG. 4 is an example of the structure of a conventional piezoelectric actuator which structure is described in Japanese Patent Laid-Open Publication No. 60-81568. Referring to FIG. 4, reference numeral 5 designates a stack of plural piezoelectric elements (PZT, for example). The stacked piezoelectric elements 5 have a property of vertically expanding when voltage is applied across the piezoelectric elements 5 by way of a lead wire (not shown). The stacked piezoelectric elements 5 are fixed between a base 4 and a connecting member 6. The piezoelectric actuator is provided with a pair of lever arms 2. The lever arms 2 are connected through a pair of hinges 3 to the base 4, and are also connected through a pair of hinges 7 to the connecting member 6. An elastic beam 1 is mounted between opposite upper free ends 2c of the lever arms 2. FIG. 4 shows a condition where no voltage is applied to the piezoeletric elements 5. Under the condition shown in FIG. 4, the elastic beam 1 is stably maintained linear.
When voltage is applied to the stacked piezoelectric elements 5, they are vertically expanded to rotate the lever arms 2 in counter directions such that the distance between both the opposite upper free ends 2c decreases. As a result, the elastic beam 1 is upwardly flexed. The elastic beam 1 is provided at its central position with a mechanically displacing member 8. Accordingly, a small amount of deformation of the piezoelectric elements 5 can be magnified by the lever arms 2 and the elastic beam 1 to thereby greatly vertically displace the mechanically displacing member 8.
The present invention relates particularly to such a piezoelectric actuator of a type capable of magnifying the amount of deformation of the piezoelectric elements by the pair of lever arms.
FIG. 5 is a plan view of the piezoelectric actuator shown in FIG. 4. The elastic beam 1 is of a substantially linear shape in plan, and it tends to be easily deformed or vibrated when a sideward external force as depicted by an arrow F is applied thereto, causing a less durability.
Such a problem of durability may be considered to be solved by increasing the width of the elastic beam 1. Such an increase in width of the elastic beam 1 requires an increase in width of the lever arms 2. However, since the lever arms 2 are members for contributing to the deformation, the increased width of the lever arms is not desired from the viewpoint of responsiveness to time.
Further, when a rate of magnification of displacement is intended to be changed in the conventional piezoelectric actuator, various lever arms and elastic beams having different sizes are necessary.